1. Field of the Invention
The present invention is directed to a propeller pod drive (pod drive) with improved radial bearings and axial bearings.
2. Related Art
Propeller pods (pods) have been used as drives in shipbuilding for some time. In contrast to conventional ship's drives, the drive elements are not accommodated in the hull of the ship, but rather outside the hull in a pod attached to the hull. Thrust screws and traction screws, as well as combinations thereof, can also be used. Aside from ships, pod drives can also be used for other watercraft such as boats, torpedoes, drones, and floating infrastructures such as drilling rigs or other large industrial or urban marine structures for locomotion, maneuvering, and/or stabilization.
The propeller shaft is often driven by an electric motor accommodated in the pod; the energy for operating the electric drive is supplied by a diesel generator, for example. Therefore, it is no longer necessary to provide a mechanical connection from the ship's diesel engine to the ship's screw by a shaft. Rather, the pod drive obtains its energy from the diesel generator by power supply lines. Therefore, the arrangement of the diesel generator is subject to far fewer constructional limitations than a conventional screw drive. However, arrangements in which the output torque of a motor accommodated in the ship's hull is mechanically transmitted to a screw driveshaft in the pod by a coupling arrangement, articulated arrangement and/or transmission arrangement are also possible.
The pod advantageously has a streamlined, watertight cladding and can be fastened to the hull to be rotatable by up to 360 degrees so that the pod drive can also take over the function formerly performed by the rudder. Owing to the fact that the ship's motor can be used for maneuvering in any azimuthal direction in a pod drive of this kind, it is possible to achieve movements and curve radii which are not possible with conventional ship's motors having a rigid axle and rudder or which are only possible with auxiliary maneuvering devices. In particular, at least rear thrusters that were formerly required for maneuvering especially between harbor and open sea can be entirely dispensed with. Pods that are rigidly arranged at the hull and arrangements having a plurality of pod drives in which some of the drives have rigid pods are also possible.
U.S. Pat. No. 2,714,866 discloses a pod drive in which the radial forces of the screw driveshaft are supported by slide bearings and the axial forces of the screw driveshaft are supported by a disk which is arranged on the shaft and is supported at guide elements or supporting elements. However, the principle of the pod drive was not put to use commercially to a significant extent until about 40 years after the appearance of this publication, i.e., in the 1990s. The slide bearing solution was not pursued further; rather, all pod drives in use today have rolling bearings. This may be because rigid slide bearings such as those proposed in the above-cited reference quickly become unusable in the event of axial misalignments, i.e., tilting of the driveshaft, due to uneven or localized wear.
However, existing solutions utilizing rolling bearings also have drawbacks which, in spite of the significant technical and economic advantages of the pod drive in theory, have so far thwarted a more widespread use of this technology. For example, the rolling bearings are loaded by extremely high tensile forces, thrust forces and weight forces and the rolling elements and running surfaces therefore experience comparatively considerable friction. On one hand, this leads to comparatively high friction losses as well as severe bearing wear, which has a direct impact on service life. Therefore, regular and frequent servicing is required to avoid failure of the bearings. The bearings are conventionally flanged to the pod structure and can only be serviced or replaced by dismantling the pod. Such work is expensive and can only be performed in dock.